Incidence of road injuries in the United States


[Download detailed results tables: USA-WebTables
Last Updated: May 5 2010

Important: Please note that the results presented here are preliminary. Additional adjustments will be necessary as the results are made consistent with the ongoing Global Burden of Disease (GBD-2005) project, for which the results presented here are an input. Final estimates of the GBD-2005 study will be released in late 2010.  

About this report

Reliable statistics of road injuries are an essential input for describing the public health burden of injuries, evaluating the impact of safety policies, and benchmarking achievements. While injury surveillance systems are common in high income countries, most low and middle income countries are unlikely to have such capacity for several decades. In the interim, estimates should be derived by harmonizing injury statistics from the wide array of data sources that may be available in a country or region. 

This report summarizes our findings for the incidence of deaths and non-fatal injuries from road crashes in USA. This report is one of a series of 18 national road injury assessments that we are producing during the course of this project. Other than USA and Spain, all other countries are low- or middle-income countries. The intended audience of these reports includes the global donor community, the international research community, and national health and transport policy makers. We are committed to keeping this project open-source and collaborative in nature. All readers are encouraged to provide feedback to help improve methods, incorporate other sources of information, and suggest more effective methods for communicating these results.


Summary Results
In 2005, road crashes resulted in 47,532 deaths in the United States representing an annual injury rate of 15.9 deaths per 100,000 people. In addition, almost 5 million people were victims of non-fatal injuries due to road crashes. The road injury death rate in the United States is higher than that in many low- and middle-income countries (Figure 1) and is 2.7 times the death rate in countries with the best road safety performance (Sweden, UK, and Netherlands). 

Injuries as a whole, including from unintentional and intentional causes, resulted in 176,406 deaths or 7% of all deaths in the United States in 2005.  

Road injuries are the leading cause of injury deaths in the United States, substantially in excess of deaths from suicides and homicides (Table 1). In 2005, road injuries account for over one-fourth of all injury deaths in the United States.  



How did we compute these estimates

Our general methodology for estimating deaths and non-fatal injuries involves piecing together data from a wide array of sources that typically include death registers, hospital records, funeral records, health surveys, and police reports. This requires filling information gaps, mapping from varying case definitions, deriving population based incidence estimates from sources that may not track denominator populations, and appropriately reapportioning cases assigned to poorly specified causes. For a general description of the broad methodology, please visit the Methods-overview section of our website.

The following sections describe the specific data sources used, the estimation methods, and the key results for our estimates of road injuries in the United States. The analytical adjustments to the data introduce uncertainty in the estimates. Thus, wherever possible, we have outlined the effects of the adjustments on the estimates. 

Overview of data sources

We estimated the incidence and distribution of road injury deaths in the United States using national death registration data obtained from the WHO Mortality Database. We also report estimates of the incidence and distribution of non-fatal injury deaths using national data for hospital admissions and outpatient visits.

Estimates of road injury deaths

Our review of data sources for estimating national road injury deaths in the United States revealed two potential data systems: national death registration data and the Fatality Analysis Reporting System (FARS) of the National Highway Traffic Safety Administration (NHTSA). In this study, we have computed estimates of national road injury deaths from the former (death registration) and compared them with those repeated by NHTSA-FARS. We obtained death registration data from the publicly available WHO Mortality Database. These data are tabulations of deaths recorded by national civil registration systems. Typically these systems record age, sex, and causes of death coded using principles of the International Statistical Classification of Diseases (ICD). 

A total of 55 years of data were available, most recently for the year 2005. We only analyzed data for the most recent nine years available (1997-2005). Data from prior years was not analyzed because it is not reported to the WHO at a level of detail that allows us to use our analytical estimation methods. In particular, almost two decades of data from the ICD-9 coding era has not been analyzed because the data was reported in the WHO Mortality Database using a condensed tabulation list (ICD-9 BTL). 

Reclassification to GBD-2005 definitions: We reclassified age into 38 age-sex groups. The age definitions match those used by the GBD-2005 project and are available on the GBD-Injury expert group website. Click here to go directly to the age definitions. 

We reclassified the ICD coded deaths to the definitions of road injuries (and other injuries) 

as recommended by the GBD-Injury expert group. The definitions are available on the expert group's website. [Click here to go directly to the external cause definitions]. These definitions map all ICD codes for external causes of injury to 48 fully-specified cause categories and 21 partially-specified and undetermined cause categories. The fully-specified cause categories include nine road-user categories:
  • Pedestrian (V01-V04, V06, V09), 
  • Bicyclist (V10-V19), 
  • Two-wheeler rider (V20-V29), 
  • Three-wheeler occupant (V30-V39), 
  • Car occupant (V40-V49), 
  • Van occupant (V50-V59), 
  • Truck occupant (V60-V69), 
  • Bus occupant (V70-V79), and,
  • Other road injury (V80, V82, V83, V84, V85). 
In addition, there are two partially-specified sub-categories of road injuries:
  • Road injury - unspecified occupant, i.e. not pedestrian or bicyclist (V87-V88), and,
  • Road injury - unspecified road user (V89, Y85.0)
Table 2 shows the distribution of the 176,401 injury deaths reported in the death registration data for the year 2005. It should be noted that the 21 partially-specified categories have a hierarchical structure of specificity and many of these categories are not related with road injuries. 

We assessed the quality of the death registration data based on the distribution of the number of deaths in the partially specified categories. As shown in Table 2, approximately one-fourthof the deaths that are specified as being from road injuries do not have a road-user specified. Furthermore, 16% of deaths among vehicle occupants do not have a vehicle-type specified. Approximately 5% of the injury deaths specified as being from unintentional injuries do not have an injury mechanism specified. This is a relatively small fraction. Our analysis of global data has found that this category can exceed 20% in many countries.  

Reallocation of injury deaths coded to partially-specified causes: The deaths classified to partially-specified and undetermined cause categories were redistributed over the fully-specified categories. All redistributions were done in proportion to the number of cases in the fully-specified causes within age-sex groups. The redistribution is done in 21 steps, one each for each partially-specified category, that respects the information content in the hierarchical structure of the partially-specified categories. Thus, several of these steps do not affect the road injury estimates.  For instance, the category of firearm:undetermined intent was  redistributed over the categories for firearm:unintentional, firearm:self-inflicted, and firearm:inter-personal, and this redistribution step has no effect on the road injury estimates. Only the redistribution of the following partially-specified categories have an effect on road injury estimates:
  • Road injury - unspecified occupant, i.e. not pedestrian or bicyclist, 
  • Road injury - unspecified road user,
  • Unspecified transport injury,
  • Unspecified unintentional injury,
  • Unspecified mechanism - undetermined intent,
  • Unspecified mechanism - unspecified intent,
The effect of these redistribution steps is evident from Figure 3. The death registration data has 45,812 deaths specified as road injuries. As expected from the distribution of deaths shown in Table 2, the only substantial increase in the estimates of road injury deaths occurs when deaths coded to unintentional injuries- unspecified mechanism are reallocated. This results in an increase of approximately 4% in the total number of road injury deaths. 

Adjustments that have not applied yet: Two key adjustments that are likely to modify the road injury death counts have not been applied yet. First, we have not reallocated deaths coded to unspecified causes outside the ICD injury chapter. This reallocation has not been done yet because research into the causes of deaths coded to this category is currently ongoing. However, it should be noted that in the United States, only a relatively small fraction (0.7%) of all deaths are coded to this category and the effect on road injury death counts is thus expected to be small. 

Second, we have made no adjustments to account for incomplete death registration because estimates of completeness of global death registration data are currently being developed. However, our preliminary comparison of total all-cause deaths reported in the death registration data analyzed by us with deaths reported by the UN Population Division suggests that death registration in the United States is near complete. It should be noted that both of these adjustments would increase the estimated death counts. Thus, the mortality results presented here likely underestimate the true number of road injury deaths.

Comparison of our estimates with other sources

Figure 3 shows our estimates of road injury deaths in the United States compared with those from NHTSA-FARS and those reported in the 2009 WHO Global Status Report on Road Safety (GSSR) for the year 2006. Our estimates for road injuries track the NHTSA-FARS estimates closely in trend but are consistently higher by approximately 10%. 






Road deaths by age and sex

Most road deaths occur among adult males (Figure 4a). Over 2/3rd (69%) of all road injury deaths were men and most of these men (70%) were adults older than 20 years. Death rates (Figure 4b) among men are over twice those among women overall. Higher death rates among men is true for all age groups but the gender differential is very small among children under 15 years.  Both death counts and death rates rise dramatically in the transition in age from childhood to young adults (see age groups 10-14 years and 15-19 years). Death rates peak in the age group of 20-24 years and then decline with age before rising again among those older than 65 years.
Such age and sex patterns in deaths and death rates are consistent with those seen in other countries. For 
the most part, the gender differentials in death rate are a result of higher exposure to road traffic among men in combination with higher risk-taking behavior. Similarly, the age pattern of death rates partly reflects patterns of exposure and partly case-fatality rates. While exposure to road traffic declines with age among older populations, the bio-mechanical tolerance to injury (i.e. the likelihood of death in the event of a crash) also declines, resulting in increasing death rates with age. 

Road deaths by type of road-user

Over half of road deaths (64%) in the United States are among car and van occupants (Figure 5). Pedestrians (16%) and two-wheeler riders (14%)  result in similar number of deaths.

The large number of deaths among motorcyclists in the United States is of special concern. Motorcycles are among the most risky modes of transport. Our analysis of death registration data for the last nine years showed that deaths among motorcycle riders have steadily risen during this period from 2383 deaths in 1997 to 6862 deaths in 2005. This rise in motorcycle deaths has offset the road safety gains among car occupants resulting in a flat trend in overall road injury death rates (Figure 3).


Estimates of non-fatal road injuries

The incidence of non-fatal road injuries can be estimated from various sources, including police reports, hospital administrative records, and population surveys. Among these, police reports are widely known to underreport road injury cases in low income countries as well as in high income countries. Thus, such estimates are best derived from medical facility records, especially in settings where these records have high population coverage and completeness.

In the United States, the incidence of hospitalized non-fatal injuries can be estimated from the Healthcare Cost and Utilization Project - Nationwide Inpatient Sample (HCUP-NIS), which provides information about over 7 million hospital inpatient stays. 

 The incidence of injuries treated in emergency departments can be estimated from the 2001 National Electronic Injury Surveillance System - All Injury Program (NEISS-AIP). Both of these databases include weights that can be applied to generate nationally representative estimates. In this report, we use estimates of the incidence of non-fatal road injury hospitalizations and emergency department visits from these two sources as reported in "The incidence and economic burden of injuries in the United States",  Eric A. Finkelstein, Phaedra S. Corso, Ted R. Miller and Associates, Oxford University Press, 2006. 

Figure 6 (a and b) shows the road-user distribution of hospitalized and non-hospitalized road injuries in the United States. Non-fatal injuries are dominated by vehicle occupants, 70% in hospitalized cases, and 76% in non-hospitalized cases. While the road-user distribution of non-fatal cases is similar to that of fatal cases, there are some differences. In particular, motorcycle riders comprise a smaller proportion of non-hospitalized cases (5%), than hospital admissions (8%), and fatal cases (14%). This pattern suggests a higher case fatality rate for motorcycle riders in the United States. Similarly, vehicle occupants comprise a higher proportion of non-hospitalized cases (76%), than hospital admissions (70%), and  fatal cases (68%), suggesting a lower case fatality rate for vehicle occupants. 

Figures 7 (a and b) shows the age- and sex- distribution of hospitalized and non-hospitalized road injuries in the United States. The high rates of non-fatal road injuries among young adult males is similar to that seen in fatalities (Figure 4). However the age- and sex- distribution of non-fatal injuries has some notable differences from the distribution of fatalities. The gender differential, i.e. the ratio of male to female incidence rate, is highest for road injury deaths (M:F ratio=2.3), followed by road injury hospitalizations (1.6), and least for non-hospitalized injuries (1.06). This pattern implies higher road injury case fatality rates for men, which may result from differentials in high-risk exposure. Similarly, the differences in age-patterns of fatal and non-fatal injuries should be noted. Road injury death rates have a bimodal peak with the highest rate among the oldest age groups. Hospitalized cases also have a bimodal distribution but the second peak among the older age groups is smaller. Finally, the non-hositalized cases have a unimodal distribution with the lowest rate among the oldest age group. This higher road injury case fatality rate among older age groups are likely due to lower biomechanical tolerance to injuries in this age group.

















Acknowledgements
These country reports were produced as part of a project funded by the World Bank Global Road Safety Facility. The results presented here are based on secondary data analysis of data collected by various national and international agencies.




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USA_webtables18May2010
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Kavi Bhalla,
Jun 3, 2010, 3:07 PM